The typical conventional reticle-holding devices (also termed reticle “pods”) are configured for holding one or more square, glass reticles each having side dimensions of, e.g., 152.4 mm (6 inches) and a thickness of several mm. Most of these conventional reticle pods have certain features that have been standardized in the industry by Semiconductor Equipment and Materials International (SEMI) for automated use with various types of wafer-fabrication equipment. Thus, these conventional reticle pods are termed reticle “SMIF” (Standard Mechanical Interface) pods, abbreviated “RSPs” in the industry. Conventional RSPs are configured for use with “optical” (deep ultraviolet) microlithography systems, which are the “workhorse” microlithography systems currently in use.
A plan view of a conventional RSP 80 is shown in FIG. 10. The depicted RSP 80 is configured to hold a single square reticle R. (Other types of conventional RSPs are configured to hold multiple reticles.) The plan profile of the RSP 80 is roughly square. The RSP 80 comprises a base 81 and a cover (door) 83. When closed relative to the base 81, the cover 83 is secured in a sealing manner to the base 81 by a standardized door-latch mechanism (not shown, but well understood in the art). The door-latch mechanism is openable using a SEMI-standardized latch-opening mechanism that can be provided on any of various systems that use or manipulate the reticle and/or the RSP. Whenever the cover 83 is secured to the base 81 in this manner, an isolated space is formed between the base 81 and the cover 83. Thus, a reticle R contained within this space is isolated from the external environment, especially from environmental particulate contamination.
Attached to the base 81 at each of the four corners of the upper surface of the base are respective reticle-receiving pads 85. Each reticle-receiving pad 85 has a substantially oval-shaped plan profile that longitudinally extends toward the center of the base 81 and presents a respective “upward”-facing reticle-contact surface. The reticle R is placed in the RSP 80 such that the four corners of the square reticle R are supported on respective reticle-receiving pads 85, as shown. For mounting purposes, the reticle R typically has a generously wide non-patterned periphery that includes the four corners of the reticle. To secure the reticle R to the base 81, each respective corner of the reticle is urged against the respective receiving pad 85 by a respective presser member (not shown) mounted to a corresponding location on the inside (“lower”) surface of the cover 83. To prevent entry of debris from the external environment into the RSP 80 while allowing pressure equalization, at least one filter 87 is provided at respective corner(s) of the base 81.
By thus holding the reticle R (usually chrome-side down) within a closed space, the conventional RSP 80 of FIG. 10 effectively isolates the reticle from contaminant debris and the like that may be present in the external environment. This isolation is especially important as the reticle is being moved from one location to another in a fabrication facility or during reticle storage for later use. As noted above, the door-latch mechanism that secures the cover 83 to the base 81 is standardized in conventional RSPs 80, allowing any of various apparatus that manipulate the RSP to open the RSP to gain access to the reticle inside.
In recent years, substantial engineering effort has been directed to the development of a practical “next-generation” microlithography system that offers prospects of producing finer pattern-transfer resolution than currently obtainable using optical microlithography. One attractive next-generation lithography (NGL) approach involves the use of a charged particle beam, such as an electron beam or ion beam, as the lithographic-energy beam. A key challenge in the development of a practical electron-beam microlithography system is configuring the system to produce the desired fine-ness of pattern-transfer resolution without sacrificing “throughput” (number of units, such as semiconductor wafers, that can be lithographically exposed by the system per unit time).
In an electron-beam (EB) microlithography system, the square, glass reticle conventionally used for optical microlithography is not used. Instead, the reticle typically is round (e.g., 200 mm in diameter) and much thinner (e.g., 0.5 to 1.0 mm) than an optical-lithography reticle. The typical shape of the EB-lithography reticle is that of a SEMI standard wafer or SEMI standard notched wafer. Almost the entire surface of the EB-lithography reticle is patterned. Since the entire pattern cannot be exposed in a single exposure “shot,” the EB lithography reticle is divided into multiple “exposure units” (usually termed “subfields”) each defining a respective portion of the pattern. The subfields are individually exposed. During exposure an electron beam is irradiated, from above, onto a selected subfield of the reticle.
Portions of the reticle that define pattern features and that actually are irradiated by the electron beam are very thin and delicate. Consequently, these portions of the reticle must not contact any other surfaces (such as a surface of a reticle pod). Rather, the reticle must be handled and supported only by its non-patterned (and more robust) peripheral “handling zone.” The handling zone of an EB-lithography reticle typically is narrow, with a maximum usable “handling” width of several mm. Either or both the “upper” and “lower” surfaces of the handling zone can contact other surfaces such as of the reticle pod.
Since conventional reticle pods, such as the RSP 80 shown in FIG. 10, are configured for holding relatively thick, square reticles for use in optical microlithography, these pods are not suitable for holding thin, round, EB-lithography reticles having a narrow peripheral “handling” width of only several mm.